The present disclosure relates to a light scanning device for forming an image through scanned exposure on a scanned face, and to an image forming apparatus, such as a copier, printer, or fax, or an all-in-one device thereof, equipped with the device.
The light scanning device employed in the image forming apparatus forms a latent image on an image carrier by scanned exposure of the surface of the image carrier. Because the image carrier undergoes scanned exposure by a light beam, when the light beam is deflected, a rotating multifaceted mirror such as a polygon mirror is rotated at high speed, and a rotating shaft of a motor that drives rotation of the rotating multifaceted mirror, as well as a bearing thereof, emit heat. Additionally, electronic control components on circuit boards, such as a drive circuit for controlling driving of the motor, emit heat as well. The heat generated by the motor and electronic control components becomes trapped inside a housing of the light scanning device, and the housing reaches high temperature. When the housing reaches high temperature, there is a risk that lenses, mirrors, and other optical members housed inside the housing will experience heat deformation together with the housing, and that, due to heat deformation of the housing and the optical members, a satisfactory latent image can no longer be formed on the surface of the image carrier.
Various techniques for holding down the rise in temperature of the light scanning device due to heat generated by the motor and electronic control components are known in the related art. In a first light scanning device, an opening is formed in a bottom part of the housing, and a substrate is attached to this opening. To a lower face side of the substrate is disposed a power section of a motor, such as a coil and magnets, and a drive circuit for driving the motor, while a rotating multifaceted mirror is secured to a motor rotating shaft passed through the substrate and projecting to an upper face side thereof. In so doing, the power section and the drive circuit of the motor, and the inside of the housing, are separated by the substrate, holding down infiltration of heat generated by the power section and the drive circuit of the motor into the housing.
A second light scanning device is equipped with a housing, a lid member providing closure to the interior of the housing, and an optical system and a motor block housed in the interior of the housing. The motor block is constituted to have a polygon motor equipped with a polygon mirror, a metal plate attached to the housing and supporting the polygon motor, and a metal cover covering the polygon motor and secured to the plate. The plate is furnished with a heat-radiating fin that is exposed to the outside through the housing. The cover is furnished with a heat-radiating fin that is exposed to the outside through the lid member, and heat generated by the polygon mirror is radiated to the outside by these heat-radiating fins.
A third light scanning device is equipped with a housing, a lid member closing off the interior of the housing, and an optical system and a motor block housed in the interior of the housing. The motor block is constituted to have a polygon mirror, a polygon motor for driving rotation of the polygon mirror, a rotating shaft of the polygon motor, and a bearing section for supporting the rotating shaft. The bearing section is attached to the housing via a motor attachment panel, and on the bottom face of the bearing section there is arranged a contact member of round columnar shape, having higher thermal conductivity and higher thermal capacity than the housing. The contact member is urged by a spring member towards the axial direction of the rotating shaft, and contacts the bottom face of the bearing section under pressure, thereby absorbing heat from the motor block, and reducing conduction of heat from the motor block to the housing.
In the first and second light scanning devices, the lenses, mirrors, and other such optical members are retained by the housing, whereas the polygon motor having the polygon mirror is retained by an intermediate member, such as a substrate, plate, or the like, the intermediate member being attached to the housing. Therefore, due to the interposition of the intermediate member, the accuracy of disposition of the optical members with respect to the polygon mirror decreases. Normally, to obtain high accuracy of disposition of the optical members and the polygon mirror, it is necessary for the accuracy of manufacturing and assembly of the members to be satisfactory, as well as for the accuracy of measurement of the positions of the members to be satisfactory. In the first and second light scanning devices, in a case of measuring the position of a retaining section for an optical member, for example, a measurement is made of the dimensions from the attachment section of the housing for attaching the intermediate member (for example, a screw hole) to the retaining section for the optical member, whereas in a case of measuring the position of a retaining section for the polygon mirror, a measurement is made of the dimensions from the attachment section of the intermediate member for attaching the housing (for example, an attachment hole opposing the screw hole) to the retaining section of the polygon mirror. A risk is presented in that, in order to measure the dimensions between the retaining sections for the optical members and the polygon mirror via the intermediate member, the accuracy with which the dimensions between the retaining sections are measured will decline. This lowers the accuracy of disposition among the optical members and the polygon mirror when the optical members and the polygon mirror are attached to the light scanning device chassis, posing the inconvenience that a satisfactory latent image can no longer be formed on the latent image carrier.
An inconvenience encountered with the third light scanning device is that the device has a large size and complex constitution, due to the arrangement of the contact member for absorbing heat from the motor block.